With the development of information technologies, display technology as a window for acquiring information has been developed rapidly. At present, the thin film transistor liquid crystal display (TFT-LCD) has become the largest display market in the globe instead of the cathode ray tube (CRT) display. As a core element for the currently most popular flat-panel display, the performance of the thin film transistor (TFT) directly impacts on the quality of the display. Development of high mobility materials becomes a focus under increasing requirements on high PPI (pixels per inch) and high refresh rate in the field of display. Although the conventional polysilicon thin film transistor has high mobility, it cannot satisfy the requirement of large-scale production due to its complicated manufacturing process and high manufacturing cost. On the other hand, the oxide thin film transistor is suitable for large-scale production, but it has low mobility which is just 10-30 cm2/Vs currently and needs to be further increased.
It is known that the calculation formula of the mobility μ of the oxide thin film transistor can be expressed as:
  μ  =            e      ⁢                          ⁢      τ              m      *      
wherein m* is an electron effective mass, τ is carrier release time.
Therefore, there are two ways to improve the mobility of the oxide thin film transistor:
(1) Increase the content of metal ions with small molecule effective mass m*. For example, in IGZO (indium gallium zinc oxide), referring to Table 1, electrons have the smallest m* in In2O3, thus In has the most predominant effect on improving the mobility of the thin film transistor. Increasing the content of In3+ ions in the oxide can improve the mobility of the oxide thin film transistor significantly. However, the In3+ ions have the largest orbital radius, and the bond energy between In3+ and O is the smallest, thus the formed In—O bond is easily broken, thereby forming some oxygen dangling bonds or redundant oxygen defects, which in turn influences the stability of the thin film transistor.
TABLE 1In—OZn—OGa—Oionic bond energyweakmediumstrongmetal ion radius0.81 Å0.74 Å0.62 Åeffective mass m*smallmediumlarge
(2) Reduce the number of defects in the oxide which impact on carrier transmission. The carrier relaxation time is most affected by the defects. Specifically, reducing the number of defects in the oxide can increase the carrier relaxation time, thereby improving the mobility of the thin film transistor.